1. Field of Invention
A suspension system for short distance repositioning tractors, often referenced as terminal tractors, isolating the shock and impact of a retractable fifth wheel and rear axle from the frame of the terminal tractor by the arrangement of a rear axle and fifth wheel boom having lift cylinders between them and joining the rear axle, a lift arm assembly and a trailing arm assembly as a singular modular unit, isolated from the frame of the terminal tractor by elastomeric bushings at a forward location and pivot point on the terminal tractor frame, with a secondary suspension located at the rear of the singular modular unit.
2. Description of Prior Art
Typically, a terminal tractor has a short wheelbase of between 110 and 116 inches. It is a cab over engine design with a one person cab, offset far to one side of the chassis. It has a medium duty diesel engine with an automatic transmission and a high reduction rear axle, the automatic transmission and the high reduction rear axle allowing the tractor to start and move a heavy load with a relatively low horsepower engine. The terminal tractor is only intended for short haul purposes in a truck depot or a yard where trailers are to be moved for short distances to and from a loading area. The steering axle is suspended from the frame with semi-elliptical leaf springs, while the rear axle is typically solidly mounted to the frame using mounting brackets and large capscrews to secure the axle. The fifth wheel, used to attach to the trailer, is mounted on a pivoted bracketry, generally referenced as a boom, which raises through hydraulics and lifts a loaded trailer or chassis for a short distance during the transport in the yard or depot.
Current industry standards in suspensions have the rear axle directly mounted to the frame of the tractor. The current standards in boom attachments use steel or bronze bushings rotating on a nominal 2″ diameter pivot shaft which floats in round holes in the frame rails, usually called sockets, near the center of the vehicle. Double acting hydraulic cylinders mounted between the frame and the boom provide a 50,000 to 70,000 pound lift capacity at the fifth wheel. Because of the extreme difference in axle weight between the unloaded condition (approximately 4,000 lbs.) of the terminal tractor and the loaded condition (approximately 30,000 lbs.), finding a working suspension that performs under both conditions has been a challenge.
The domestic terminal tractor manufacturers have been trying to develop a dependable working suspension for the rear axle of terminal tractors for several years. In the early 1980s, rubber block suspensions were attempted to cushion the frame from the shocks of ground impacts, but they provided very little flexibility. Since about the middle 1980s, several manufacturers have offered versions of conventional spring suspensions fitted to provide limited flexibility in empty and light load conditions and to settle the frame on rubber bumpers above the axle under heavy load conditions. This system is complex and expensive, but seems to be the best suspension alternative to date. Since 1992, a company named Capacity has offered a rear axle air suspension option, featuring a large A-frame under the chassis, connected to a central frame cross-member approximately below the boom attachment point near the center of the vehicle. The rear axle and lift cylinders attach to the rear ends of the A-frame below the chassis. Air springs between the axle and the frame allow vertical movement of the rear axle relative to the frame, lift the boom from the A-frame, independent of the chassis, which allows effective isolation of the chassis from vertical movement of the rear axle and boom. A bushed single front attachment of the A-frame suggests allowance of side-to-side rotation of the axle relative to the frame. However, solid mounting of the lift cylinders to the fifth wheel boom, solidly pinned to the frame through a steel pivot shaft and bushings prevents side-to-side suspension rotation and creates extreme high stress loads at the A-frame connection, pivot shaft mountings and bushings. The cost, weight and complexity of this suspension are significant and it has proven to be expensive to maintain and service. This type product accounts for only a small percent of the market.
The following United States patents were discovered and are disclosed within this application for utility patent. In U.S. Pat. No. 6,209,895 to Mueller, an axle suspension is provided for a wheeled vehicle having an axle suspension pivotally engaged with the frame with a rubber bushing acting as cushion along with a shock relating between the frame and rear axle mount. In U.S. Pat. No. 6,135,483 to Metz, a fifth wheel suspension system is disclosed wherein the frame has three separate pivotal mounting locations, having a first pivotal mount located between the frame and a rear axle support arm having an attached rear axle, with a bushing for a cushion and a shock, similar to Mueller, supra. This suspension system also contains pivotal mountings between the frame and two fifth wheel lift arms, with a hydraulic cylinder between the rear axle support arm and the base of the fifth wheel. This still relates shocks of the rear axle directly to the fifth wheel and also to the three pivotal connections to the frame.
Several patents use air suspension systems in a variety of pivotal mounting mechanisms for fifth wheels, including U.S. Pat. No. 2,821,409 to Chalmers, U.S. Pat. No. 3,380,758 to Granning, U.S. Pat. No. 5,388,849 to Arsenault, U.S. Pat. No. 4,279,430 to Tagg, and U.S. Pat. No. 5,639,106 to Vitale. Those using rubber bushings for cushion between related pivotal components having fifth wheel application included U.S. Pat. No. 4,162,799 to Willetts, U.S. Pat. No. 5,346,247 to Snyder and U.S. Pat. No. 5,655,788 to Peaker. None of the suspension systems include a singular pivot point between the frame, the rear axle and the fifth wheel boom which singularly isolate the frame from the rear axle and the fifth wheel boom, yet provide a secondary suspension between the frame and the fifth wheel boom under heavy load as well as a no-load situation.